Development of fibrocartilage layers in the anterior cruciate ligament insertion in rabbits

Histological differences in cartilage layer growth at various tendon and ligament insertions in rabbits

Objectives: Histological differences in cartilage layer growth in Achilles tendon (AT), quadriceps tendon (QT), patellar tendon (PT), and anterior cruciate ligament (ACL) insertion are unclear. Therefore, this study aimed to investigate the differences in cartilage layer growth in AT, QT, PT, and ACL insertions. Materials and Methods: Forty-eight male Japanese white rabbits were used. Six animals were euthanized at different stages (day 1 and 1, 2, 4, 6, 8, 12, and 24 weeks). Safranin O-stained glycosaminoglycan (GAG) production area, chondrocyte count, and insertion width were investigated. Results: A two-way analysis of variance (ANOVA) revealed a significant difference in the main effects of time and insertion for all parameters. In addition, the time × insertion interaction was significant. Multiple comparisons showed a significant difference between the ACL insertion and all other variables; however, the GAG production area was not significantly different for the QT, PT, and AT insertions. AT insertions were significantly different from all other groups; however, the number of chondrocytes and insertion width were not significantly different for ACL, QT, and PT insertions. Conclusion: Cartilage layer growth differed between the AT, QT, PT, and ACL insertions. The differences between the insertions may also be due to the differences in their structures, locations, and mechanical environments.

Influence of periostin on the development of fibrocartilage layers of anterior cruciate ligament insertion

BACKGROUND

Periostin (Postn) is thought to play a role in the formation of anterior cruciate ligament (ACL) insertion. However, the influence of Postn on the development of ACL insertion requires further understanding. This study aimed to clarify the influence of Postn on the development of fibrocartilage layers of ACL insertion.

HYPOTHESIS

We hypothesized that Postn would influence the development of fibrocartilage layers of ACL insertion.

MATERIALS AND METHODS

C57BL/6N wild-type (Postn+/+; n=54) and Postn knockout (Postn-/-; n=54) mice were used in this study. Six animals were euthanized at 1 d and 1, 2, 3, 4, 6, 8, 10, and 12 weeks of age in each group. The chondrocyte number, proliferation, apoptosis, safranin O-stained glycosaminoglycan (GAG) area, type II collagen staining area, tidemark length, and insertion width were evaluated.

RESULTS

Chondrocyte proliferation was high up to 2 weeks in Postn+/+, while low at age 1 d; it was, especially lower in Postn-/- than in Postn+/+ at age 1 d and 1 week. Chondrocyte apoptosis was high up to age 8 weeks in Postn+/+ and at 6 weeks in Postn-/-; it was especially higher in Postn-/- than in Postn+/+ at age 1 week. The GAG stained area was thickest for age 1 d to 4 weeks in Postn+/+ and for age 2 to 6 weeks in Postn-/-. The type II collagen staining area in Postn+/+ was thicker than that in Postn-/- at age 6 and 8 weeks. The tidemark length in Postn+/+ was longer than that in Postn-/- from age 8 to 12 weeks. The insertion width in Postn+/+ was longer than that in Postn-/- from age 1 to 3 weeks.

DISCUSSION

Postn decreased cell proliferation in the early postnatal phase and influenced the development of the fibrocartilage layer extracellular matrix of ACL insertion in mice. Postn may contribute to the development of methods for regeneration of the ACL insertion.

LEVEL OF EVIDENCE

V; controlled laboratory study.

Periostin Contributes to Fibrocartilage Layer Growth of the Patella Tendon Tibial Insertion in Mice

Background and Objectives: The influence of periostin on the growth of the patella tendon (PT) tibial insertion is unknown. The research described here aimed to reveal the contribution of periostin to the growth of fibrocartilage layers of the PT tibial insertion using periostin knockout mice. Materials and Methods: In both the wild-type (WD; C57BL/6N, periostin +/+; n = 54) and periostin knockout (KO; periostin −/−; n = 54) groups, six mice were euthanized on day 1 and at 1, 2, 3, 4, 6, 8, 10, and 12 weeks of age. Chondrocyte proliferation and apoptosis, number of chondrocytes, safranin O-stained glycosaminoglycan (GAG) area, staining area of type II collagen, and length of the tidemark were investigated. Results: Chondrocyte proliferation and apoptosis in KO were lower than those in WD on day 1 and at 1, 4, and 8 weeks and on day 1 and at 4, 6, and 12 weeks, respectively. Although the number of chondrocytes in both groups gradually decreased, it was lower in KO than in WD on day 1 and at 8 and 12 weeks. In the extracellular matrix, the GAG-stained area in KO was smaller than that in WD on day 1 and at 1, 4, 8, 10, and 12 weeks. The staining area of type II collagen in KO was smaller than that in WD at 8 weeks. The length of the tidemark in KO was shorter than that in WD at 4 and 6 weeks. Conclusion: Loss of periostin led to decreased chondrocyte proliferation, chondrocyte apoptosis, and the number of chondrocytes in the growth process of the PT tibial insertion. Moreover, periostin decreased and delayed GAG and type II collagen production and delayed tidemark formation in the growth process of the PT tibial insertion. Periostin can, therefore, contribute to the growth of fibrocartilage layers in the PT tibial insertion. Periostin deficiency may result in incomplete growth of the PT tibial insertion.

Stem cell sheet interpositioned between the tendon and bone would be better for healing than stem cell sheet overlaid above the tendon-to-bone junction in rotator cuff repair of rats

BACKGROUND

Although stem cells might enhance natural enthesis healing in surgical rotator cuff repair, not much attention has been given to the delivery and location of delivering stem cells. The purpose of this study to know where to locate those stem cells during repair.

METHODS

Animal model of chronic rotator cuff tear was created in 24 rats. Adipose-derived stem cells were engineered as a sheet and transplanted 1) between a torn tendon and humerus (interposition group) or 2) over a repaired tendon-to-bone junction (overlay group) at the time of surgical repair. Tracking of stem cells with overexpression of green fluorescent protein (GFP) were carried out at the time of sacrifice in additional 4 shoulders in each group. Histological and Biomechanical evaluation was performed to compare the differences in tendon-to-bone healing.

RESULTS

Histology showed increased fibrocartilage, a clear boundary at the mineralized fibrocartilage, abundant collagen type III, and higher total scores, especially in the interposition group. GFP-overexpression was observed at the transplanted site at 2 weeks after repair. Although two groups where stem cell sheets applied showed higher load to failure than the repair-only group, the load to failure was not different between the interposition and overlay group.

CONCLUSION

In the chronic rotator cuff repair model, stem cell sheets enhanced regeneration of the tendon-to-bone junction. This regeneration was effective when the stem cell sheet was interpositioned at the tendon-to-bone interface.

LEVEL OF EVIDENCE

Basic Science Study; In Vivo Animal Model; Histology and Biomechanics.

Development of fibrocartilage layers in Achilles tendon enthesis in rabbits

Objective: The details regarding the development of fibrocartilage layers in Achilles tendon (AT) enthesis are unknown. Therefore, we evaluated the development of fibrocartilage layers in AT enthesis using a rabbit model.

Materials and Methods: Forty-eight male Japanese white rabbits were used in this study. Six of them were euthanized at different stages (day 1, and 1, 2, 4, 6, 8, 12, and 24 weeks of age). The proliferation, apoptosis, Sox9-positivity rates, and chondrocyte number were evaluated. Additionally, safranin O-stained glycosaminoglycan (GAG) areas, width of AT enthesis, and calcaneus length were assessed. All parameters were compared to those at 24 weeks of age.

Results: The level of chondrocyte apoptosis was high from 1 to 8 weeks of age, and high expression level of Sox9 was maintained from day 1 to 6 weeks of age, which decreased gradually. Safranin O-stained GAG areas increased up to 12 weeks, calcaneus length increased up to 6 weeks, and the width of AT enthesis increased up to 1 week of age.

Conclusion: The changes in chondrocyte and extracellular matrix were completed by 8 and 12 weeks of age, respectively. The development of fibrocartilage layers in AT enthesis was completed by 12 weeks of age. Our results contribute to the administration of appropriate treatments based on age and aid in the development of novel methods for regenerating AT enthesis.

Differences in the Development of Fibrocartilage Layers in the Quadriceps Tendon and Patellar Tendon Insertions in Rabbits: A Quantitative Study

Background

Differences in the development of fibrocartilage layers in quadriceps tendon (QT) and patellar tendon (PT) insertion sites are unclear. Because the mechanical environments for the QT and PT are different, the development of the QT and PT insertions may differ.

Purpose

To investigate differences in the development of fibrocartilage layers in the QT and PT insertion sites in rabbits through use of quantitative morphometric evaluations.

Study Design

Descriptive laboratory study.

Methods

This study included 54 male Japanese White rabbits. Animals were euthanized at ages 1 day and 1, 2, 3, 4, 6, 8, 12, and 24 weeks (n = 6 for each age). Chondrocyte number, proliferation, apoptosis, sex-determining region Y box 9 (Sox9)-positive rates, safranin O-stained glycosaminoglycan (GAG) areas, tidemark length, insertion width, and patellar length were evaluated and compared with the same parameters at age 24 weeks and between QT and PT insertion sites.

Results

Chondrocyte proliferation was low up to age 2 weeks for QT insertion and low up to 1 week for PT insertion. Chondrocyte apoptosis was high at 1 day and Sox9 expression was low up to 1 week for PT insertion. Sox9 expression was higher in QT than in PT insertion at age 12 weeks. The high chondrocyte count continued to age 1 day in PT insertion and up to 6 weeks in QT insertion. The chondrocyte number was higher in QT than in PT insertion at age 2 weeks. The period of thicker GAG lasted from 2 to 8 weeks in PT insertion and from 1 to 12 weeks in QT insertion. GAG thickness in QT insertion was higher than in PT insertion at age 4 and 12 weeks.

Conclusion

Development of fibrocartilage layers in QT and PT insertion sites was completed at age 24 weeks in rabbits. However, the period of high chondrocyte count and period of thicker GAG were longer in QT than in PT insertion up to 12 weeks.

Clinical Relevance

Development of fibrocartilage layers in QT and PT insertions differed in rabbits. Our results may contribute to the development of appropriate treatments based on age and the development of methods for regeneration of the insertion.